The heroes can change into past heroes (Rider Cards for Decade and Ranger Key for Gokaiger).

However, Decade couldn't transform into past Riders at start.

The series starts off with a war (Rider War in Decade and Legend War in Gokaiger).

Interestingly, the first 34 Sentai teams would battle Zangyack which the battle ends with the team sacrificing their powers in order to defeat Zangyack while various Riders in the Heisei series battles Decade which the battle concludes with Decade overpowering the Riders.

The final forms are similar (Decade's Complete Form and Gokai Silver's Gold Mode).

The heroes meets characters from past series.

Although in Decade, the characters would meet the original Riders (or past characters) as their alternate incarnation, but few original Riders would appear in series or movies.